Susannah E. Walsh

Ortho-phthalaldehyde: a possible alternative to glutaraldehyde for high level disinfection

Ortho‐phthalaldehyde (OPA) was tested against a range of organisms including glutaraldehyde‐resistant mycobacteria, Bacillus subtilis spores and coat‐defective spores. Glutaraldehyde (GTA) and peracetic acid (PAA) were tested for comparative purposes. Both suspension and carrier tests were performed using a range of concentrations and exposure times. All three biocides were very effective (≥ 5 log reduction) against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa in suspension tests. OPA and GTA (PAA was not tested) were also very effective against Staph. aureus and Ps. aeruginosa in carrier tests. OPA showed good activity against the mycobacteria tested including the two GTA‐resistant strains, but 0·5% w/v OPA was found not to be sporicidal. However, limited activity was found with higher concentrations and pH values. Coat‐defective spores were more susceptible to OPA, suggesting that the coat may be responsible for this resistance. The findings of this study suggest that OPA is effective against GTA‐resistant mycobacteria and that it is a viable alternative to GTA for high level disinfection.

A NOTE: Ortho-Phthalaldehyde: proposed mechanism of action of a new antimicrobial agent

Ortho‐phthalaldehyde (OPA) is a new aromatic dialdehyde antimicrobial agent, the mechanism of action of which has been little studied. The aims of this paper are to examine what is currently known about its mechanism of action, to compare the action with that of a widely investigated aliphatic dialdehyde, glutaraldehyde (GTA), and to put forward a hypothesis that would, in the light of current knowledge, explain how OPA inactivates micro‐organisms, including GTA‐resistant Mycobacterium chelonae.

Studies on the mechanisms of the antibacterial action of ortho-phthalaldehyde

The reaction of ortho‐phthalaldehyde (OPA) with amino acids and proteins was investigated as a possible mode of action. Bacterial pellets (obtained by centrifugation) changed colour after exposure to OPA. These colours were more intense at alkaline than acidic pH. Acidic and alkaline OPA reacted with primary amino acids to form coloured products. The reaction rate accelerated with increasing pH. OPA increased the optical density of bacterial cell suspensions (an indication of protein coagulation or microbial surface or other changes in the opacity of cell constituents). The inhibition of ethylenediaminetetraacetic acid‐ and sodium lauryl sulphate‐induced lysis was not as great as for glutaraldehyde (GTA), possibly indicating less cross‐linking of amines. Interactions with primary amino groups of the outer envelope or cell wall probably play a part in the action of OPA but the level of cross‐linking associated with the outer membrane does not appear to be as extensive as that of GTA. The aromatic component might allow OPA to penetrate the outer layers of cells, thus helping to explain the very high activity of OPA against Gram‐negative vegetative organisms even though the degree of cross‐linking seems to be less than that seen with GTA. Thus, OPA reacts strongly with primary amines and stabilizes, to some extent, the outer membrane and cell walls of vegetative organisms and this probably accounts for part, but not necessarily all, of its lethal action.

Possible mechanisms for the relative efficacies of ortho-Phthalaldehyde and glutaraldehyde against glutaraldehyde-resistant Mycobacterium chelonae.

Aims: This investigation compared glutaraldehyde (GTA)‐sensitive and ‐resistant strains of Mycobacterium chelonae and examined the effects of pretreatment of GTA‐sensitive and ‐resistant strains of Myco. chelonae with chemical agents that interfere with cell wall synthesis.

Microneedle Coating Techniques for Transdermal Drug Delivery

Drug administration via the transdermal route is an evolving field that provides an alternative to oral and parenteral routes of therapy. Several microneedle (MN) based approaches have been developed. Among these, coated MNs (typically where drug is deposited on MN tips) are a minimally invasive method to deliver drugs and vaccines through the skin. In this review, we describe several processes to coat MNs. These include dip coating, gas jet drying, spray coating, electrohydrodynamic atomisation (EHDA) based processes and piezoelectric inkjet printing. Examples of process mechanisms, conditions and tested formulations are provided. As these processes are independent techniques, modifications to facilitate MN coatings are elucidated. In summary, the outcomes and potential value for each technique provides opportunities to overcome formulation or dosage form limitations. While there are significant developments in solid degradable MNs, coated MNs (through the various techniques described) have potential to be utilized in personalized drug delivery via controlled deposition onto MN templates.

Brushes and picks used on nails during the surgical scrub to reduce bacteria : a randomised trial

Though brushes are no longer used on the hands and forearms during the surgical scrub, they are still widely used on the nails. The aim of this study was to determine whether nail picks and nail brushes are effective in providing additional decontamination during a surgical hand scrub. A total of 164 operating department staff were randomised to undertake one of the following three surgical hand-scrub protocols: chlorhexidine only; chlorhexidine and a nail pick; or chlorhexidine and a nail brush. Bacterial hand sampling was conducted before and 1h after scrubbing using a modified version of the glove juice method. No statistically significant differences in bacterial numbers were found between any two of the three intervention groups. Nail brushes and nail picks used during surgical hand scrubs do not decrease bacterial numbers and are unnecessary.

New platforms for multi-functional ocular lenses: Engineering double-sided functionalized nano-coatings

Abstract A scalable platform to prepare multi-functional ocular lenses is demonstrated. Using rapidly dissolving polyvinylpyrrolidone (PVP) as the active stabilizing matrix, both sides of ocular lenses were coated using a modified scaled-up masking electrohydrodynamic atomization (EHDA) technique (flow rates variable between 5 and 10 µL/min, applied voltage 4–11 kV). Each side was coated (using a specially designed flip-able well) selectively with a pre-determined morphology and model drug substance. PVP nanoparticles (inner side, to be in contact with the cornea, mean size <ca.100 nm) were encapsulated with a probe (flourescein dye) and PVP nanofibres (outer side, to be exposed to air and eye lid, mean width size <ca.200 nm) were encapsulated with chloramphenicol (5 w/w% PVP). Release of the probe and anti-microbial activity (using Staphylococcus aureus NCTC 6571) were demonstrated based on rapid dissolution and contact of PVP model substance matrix. Adapting these findings further for advanced EHDA technologies (encapsulation layering, controllable size and deposition and multi-phase media deposition options) and intrinsic material properties (functional polymers/excipients and advanced controlled release strategies) suggests several therapeutic platforms for ocular lenses can be further developed at ambient temperature and pressure. These provide multi-functional properties (in personalized delivery, nanomedicine and nanosensors) from a single drug delivery device.

A fresh look at preoperative body washing

National guidelines do not support preoperative body washing to reduce surgical site infections, instead recommending bathing or showering with soap. Yet preoperative body washing continues to be widely used in many hospitals across Europe. This paper suggests that existing trials of preoperative body washing, upon which guidelines are based, are dated and proposes a new investigation of preoperative body washing using modern definitions of surgical site infection with standardised patient follow up, modern surgical techniques and well designed trials. This paper provides a critique of existing guidelines and describes a randomised trial with 60 participants to compare the effect of soap and two antiseptic washing products on colony forming units (CFUs) for up to six hours. Chlorhexidine gluconate and octenidine were significantly more effective than soap in reducing CFUs in the underarm, and chlorhexidine was significantly more effective than soap in reducing CFUs in the groin.

Comparison of antimicrobial textile treatments

Hospital acquired infection incidence is growing worldwide and textiles with antimicrobial treatments as a preventive measure are becoming common place. Currently tests are performed in wet conditions as encountered in wound dressings but not at 25C and 50%RH where clothing is worn. An interdisciplinary approach has modified test procedures to compare the antibacterial efficacies of textiles at these new conditions. Results demonstrated that certain fabrics with high efficacy claims fail the modified test method. IBRG membership is helping develop a new standard method for this type of fabric for the healthcare sector to enhance quality of life.

Antimicrobial activities of hydrogen peroxide and its activation by a novel heterogeneous Fenton’s‐like modified PAN catalyst

Aims:  To investigate the potential activation of hydrogen peroxide by a novel catalyst, reducing the concentration of hydrogen peroxide required and the time taken for microbial inactivation.